European Foulbrood – EFB

EUROPEAN FOULBROOD – EFB

Cause: A bacteria known as Melissococcus pluton. All castes are susceptible to EFB.

Effect: European foulbrood is most common in the spring and early summer, but it occasionally stays active through summer and fall. A good nectar flow hastens recovery. In severe cases, colonies are seriously weakened or killed. Usually the worker bees remove dead brood, but in some weak colonies it will accumulate.

Symptoms: European foulbrood infected larvae lose their plumpness and white color. They become a dull white (gray). A faint yellow might also appear on the larvae before death.

Most larvae die while coiled on the bottom of open cells. Many also die at the age when they would normally be spinning their cocoons. Few larvae die while fully extended. Larvae dead of European foulbrood, therefore, are usually coiled on the bottom of the cells, but may be irregularly twisted or fully extended.

The appearance of the dead larvae changes gradually during decay and drying. The gray and the yellow color deepen during decay, but the depth of color in scales varies considerably. Larvae that die before the cells are sealed dry rapidly, and decay is soon stopped; hence these scales are usually light colored. Larvae that die after the cells are sealed usually become dark brown or nearly black.

For a short time after death, larvae can be removed from the cells without tearing the skin. Within a few days the skin and other tissues become soft. The larvae settle against the lower wall of the cells and appear moist, melting, and flattened. At this stage of decay they are somewhat translucent and watery and cannot be removed whole. Upon drying, they become pasty and finally rubbery. Scales with European foulbrood usually do not cling closely to the cell walls and are easy to remove.

Larvae that die of European foulbrood in sealed cells may sometimes become ropy and resemble larvae dead of American foulbrood. Since the bees remove dead brood from open cells first, it sometimes happens after disease ceases to be active that the brood which died in sealed cells is all that remains in the combs. When this happens, it may be difficult to tell whether American foulbrood or European foulbrood or both of these diseases are present.

Spread: The organism Melissococcus pluton become mixed with the food fed to the young larvae by the nurse bees, multiplies rapidly within the gut of the larvae, and can cause death within about 4 days after egg hatch. House bees cleaning out the dead larvae from the cells distribute the organism throughout the hive. Since the honey of infected colonies and the beekeeper’s equipment are undoubtedly contaminated, subsequent spread of the disease is accomplished by robber bees, exposure of contaminated honey by the beekeeper, interchange of contaminated equipment among colonies, and perhaps to some extent, by drifting bees.

Control: Colony stresses can be factors in the disease’s appearance. Management to ensure strong, healthy colonies may help prevent EFB.

Use Terramycin per label directions. Requeening colonies may also help.

Prepared by:

Gordon RudloffState ApiaristOhio Department of Agriculture

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